This invention relates generally to silicon based photoresist compositions that can be used in forming low k dielectric constant materials suitable for use in electronic devices, methods of their use and the electronic devices made therefrom.
As electronic devices become smaller, there is a continuing desire in the electronics industry to increase the circuit density in electronic components, e.g., integrated circuits, circuit boards, multichip modules, chip test devices, and the like without degrading electrical performance, e.g., crosstalk or capacitive coupling, and also to increase the speed of signal propagation in these components. One method of accomplishing these goals is to reduce the dielectric constant of the interlayer insulating material used in the components.
Siloxane based materials have been identified and used as low k materials for reducing the dielectric constant of such interlayer insulating material. Generally a siloxane layer is deposited onto a substrate followed by photolithographic processes which provide a siloxane based pattern after etching, into which metal lines, vias and other electronic components may be placed. Recently siloxane compositions which are photoimageable have been disclosed, wherein a photosensitive initiator reacts with the siloxane material, such as a functional siloxane polymer, when exposed to actinic radiation thereby altering its solubility to a developer.
Many siloxane polymers in these applications are characterized by a very low glass transition temperature (Tg) which results in liquid or tacky siloxane layers which are very difficult to process. Attempts to provide siloxane polymers with a high Tg and thus tack free coatings has resulted in brittle layers which are easily cracked, limiting both their use and the thicknesses which can be achieved. Hybrid silicon-carbon polymer systems have been proposed which address brittleness in interlayer dielectric coatings for microcircuit applications. U.S. Pat. No. 6,251,486 to Chandross et al disclose a modified methylsilsesquioxane composition for use as a low dielectric material. The methylsilsesquioxane includes dimethyl and phenyl pendant groups to provide better crack resistance than an all methylsilsesquioxane. Thus, crack resistance is achieved for the coated article through incorporation of the pendant groups into the polymer prior to coating. Addition of dimethylsiloxane to silicon polymers, however, results in tacky coatings. Flexibility of siloxane coatings has been obtained by additive functionalized polymers which crosslink with the siloxane polymer during exposure. The functionalized polymers suitable in these compositions are generally water insoluble which can lead to problems during development including scumming or overdevelopment of the image when trying to remove the scum. Coating thicknesses of siloxane compositions are low due, in part, to the low viscosity achievable with these components. Typically, adding more siloxane to the composition to increase solids is hampered by stability issues, as well as a limit on the viscosity attainable.
Thus there is a need for low k dielectric photoresists which are flexible, tack free, capable of forming thick coatings and readily developable with out degrading the resulting image.